With improvement in high performance of a photographing lens such as a zoom lens unit which is capable of changing the focal distance and in downsizing according to the user's demand as to an image pickup apparatus such as a digital camera, there are increasing types of image pickup apparatus employing a so-called collapsing photographing lens unit in which lens cylinders are collapsed within a body of the image pickup apparatus when photographing is not carried out. Furthermore, since not only a simple reduction in dimensions but also a further reduction in a thickness of the image pickup apparatus are also demanded, it is now important to reduce the thickness of the lens barrel portion in a collapsed state.
As a technology to cope with the demand for reduction in the thickness of the image pickup apparatus, a construction has been used, in which the lens cylinders are collapsed into the body of the image pickup apparatus when the photographing is not carried out and in which a part of the lenses is evacuated from an optical axis of the lenses in photographing, when the lens cylinders are collapsed. Such a technology is disclosed, for example, in JP-A 2003-315861 and in JP-A 2003-149723. According to the structures disclosed in these Japanese unexamined patent application publications, since a part of the lenses is evacuated from the optical axis when the lens cylinders are collapsed, the dimension of the entire lenses in a direction of the optical axis can be reduced in the collapsed state, so that the thickness of the image pickup apparatus can be reduced.
However, in the structures disclosed in JP-A 2003-315861 and JP-A 2003-149723, the position of the lens evacuated from the optical axis is substantially within that lens cylinder which has the maximum outer diameter. Therefore, the lens cylinders contribute to reduction in thickness of the image pickup apparatus when the lenses are collapsed, but the outer diameter of the lens barrel increases. When compared with a case where the lens is not evacuated from the optical axis, since the outer diameter of the lens cylinders increase, the dimensions of the lens cylinders, in particular, the dimensions of the lens cylinders as viewed in a plane orthogonal to the optical axis increase, As a result, there is a problem that the dimensions of the image pickup apparatus, in particular, the dimension as viewed from a front side of the image pickup apparatus increases.
RICOH. CO. LTD. proposed in Japanese Patent Application No. 2005-044909 (not published) a lens barrel in which the thickness of an image pickup device can be made smaller without increasing the size of the image pickup device. The lens barrel described in comprises a plurality of lens retaining frames holding a plurality of lens groups, respectively. Among the lens retaining frames, a retractable retaining frame is included, which is adapted to retract at least one lens of at least one lens group from the optical axis of the other lens groups when shifting a collapsed state. The retractable lens retaining frame is supported, by main-guide shaft member parallel to the optical axis of the other lens groups, movably in a longitudinal direction of the main-guide shaft member and rotatably around the axis of the main-guide member. A compression torsion spring provided around the main-guide shaft member gives to the retractable lens retaining frame a rotation-urging force toward the optical axis of the other lens groups as well as an urging force in a collapsing direction along the optical axis.
The location of the optical axis of the lens retained by the retractable lens retaining frame on photographing is defined through the retractable retaining frame is defined when the retractable lens retaining frame is brought into contact with an auxiliary shaft member, by means of the rotation urging force of the spring, for guiding the retractable lens retaining frame along the optical axis of the other lens groups. On the other hand, the retractable lens retaining frame is turned around the main-guide shaft member against the rotation urging force of the spring when being collapsed such that the lens retained by the retractable lens holding frame may be retracted outside the maximum outer diameter of the lens barrel. Thereby, the increase in the outer diameter of the lens barrel can be more suppressed as compared with a conventional case in which the retracted position of the retracted lens is inside the maximum outer diameter of the lens barrel.
However, according to the invention described in Japanese patent application No. 2005-044909, the axis of the lenses is out of alignment on photographing, when the retractable lens retaining frame receives vibration and this vibration swings the retractable lens refraining frame in direction of leaving the auxiliary guide shaft member over the rotation urging force of the compression torsion spring. It may be considered that a restraining member is provided to prevent the auxiliary guide member of the restraint lens retaining frame on photographing, vibration of the retractable lens retaining frame is prevented in the state that the retractable lens retaining frame is held in between the restraining member and the auxiliary guide shaft member. In this case, the restraining member needs to be newly provided, resulting in completed construction.